As is known, apparatus for extracorporeal treatment of blood comprise, in use configuration, an extracorporeal circuit through which blood taken from a patient is sent towards a treatment unit before being returned to the patient.
A typical extracorporeal circuit comprises a blood removal branch (taking blood from the patient) which is connected to a first chamber of a treatment unit, and a second branch, a return branch, which is connected to an outlet of the first chamber and returns the blood to the patient. A pump operates at the first and/or the second branches, which pump is predisposed to move the blood through the circuit.
In a most typical configuration, the pump, for example a peristaltic pump, acts on a tract of the removal branch line upstream of the treatment unit. The treatment unit also comprises a second chamber, separated from the first chamber by a semi-permeable membrane, towards which the solid particles and the excess liquid to be removed from the patient's blood are drawn.
Also known are some therapies or treatments which can be carried out with the apparatus of the above-described type which require use of one or more infusion lines of liquids of various natures, according to the type of treatment being carried out. An infusion line typically comprises a source of liquid to be infused (for example a bag or preparation circuit in the liquid line), an infusion tube which can be associated to a pump or another flow-regulating organ, and an infusion point which can be directly connected to the cardiovascular system of the patient or to a predetermined point in the extracorporeal circuit.
Reference is made in particular to pre-dilution infusion, when the infusion line is connected to the blood removal branch upstream of the treatment unit, and to post-dilution infusion, when the line is connected to the blood return branch to the patient.
Independently of the type of treatment carried out and of the presence and configuration of the infusion lines, a value which it is important to know is the effective flow rate of the blood removed from the patient and treated by the machine. Normally the operator sets the flow rate and the machine displays the set flow-rate, checking that the actual flow rate follows, with a certain degree of approximation, the set rate. Normally the blood circuit is provided with a flow sensor which acts on the extracorporeal circuit and is able to provide a signal to send to a control unit which regulates the blood pump. For example, the blood pump can be associated to a revolution counter, or angular velocity sensor, able to generate a signal which is then processed by the control unit to provide an indication of the blood flow and thus the pump speed can be corrected, if necessary.
The applicant has found that there are certain configurations in which the total flow rate when calculated as described above does not provide a datum relating to the flow rate actually as removed from the patient; for example, a particular configuration is achieved when the blood pump operates in a tract of the blood removal branch while a pre-dilution infusion line is connected to a portion of the blood removal branch upstream of the tract of tubing in which the pump operates.
In this configuration a reading of the blood flow rate effectively taken from the patient based on the angular velocity of the pump leads to a wrong calculation: it is indeed true that the liquid crossing the tract of tubing in which the pump operates comprises blood coming from the patient plus liquid coming from the infusion line or lines which are connected to the tract of tubing upstream of the blood pump.
More generally, when the calculation of the blood flow rate taken from the patient and treated in the extracorporeal blood circuit is derived from a sensor and/or control unit acting in a tract of tubing in the extracorporeal circuit which is located downstream of a point where a liquid line enters the circuit, the flow rate of the liquid line causes an error in the calculation of the blood flow rate.
A main aim set by the applicant is thus to calculate by a simple method a blood flow rate which is effectively that which is removed from the patient, in cases where there is an infusion line placed as described above.
A further aim is to provide a technical solution which is able automatically to guarantee a desired flow rate in a blood removal operation on a patient, independently of the presence of any liquid infusion upstream of the means destined to cause the liquid to circulate in the extracorporeal circuit.
A further aim of the invention is to provide a device which informs about and controls the ratio between the true blood flow rate extracted from a patient and the flow rate of any line destined to flow into the extracorporeal circuit upstream of the blood pump.
A further aim is to provide a simple device which operates with traditional sensor means, present in apparatus for blood treatment.
In addition to the foregoing, a further aim of the invention is to provide a device which operates both in the case where the flow rates of the blood pump and the pre-infusion lines are predetermined by the user, and in the case where one or more of the flow rates are not predetermined.
One or more of the above-mentioned technical aims are attained by a device for determining a blood flow rate in an extracorporeal blood circuit and by an apparatus for extracorporeal blood treatment comprising the infusion device, according to what is described in one or more of the appended claims.